The invention relates to a method for the efficient dissemination of information in a satellite navigation system.
Satellite systems for global navigation (GNSS; GNSS=global navigation satellite system) and/or satellite navigation systems are used for position finding and for navigation on the ground and in the air. GNSS systems, such as the European satellite navigation system that is currently under construction (hereinafter referred to as the Galileo system or simply Galileo), comprise a plurality of satellites, an earth-based receiver system, which is connected to one or more central processing center(s), of observation systems (ground infrastructure), and utilization systems, which evaluate and use the satellite signals, transmitted by radio from the satellites, in particular for navigation. In a satellite navigation system there is a continuous exchange of information between the satellites and the ground infrastructure as well as within the components of the ground infrastructure, in order to guarantee a reliable and continuous operation of the satellite navigation system. In this respect it is especially important that information about the availability of the system arrives at the utilization systems without prolonged time delays, in order, for example, to warn the users about faulty signals, which could have an adverse effect on the accurate detection of a user's position.
An accurate position detection demands both local as well as global integrity in the satellite navigation system. Integrity means in particular that the satellite navigation system is capable of warning a user within a certain period of time when parts of the system are not to be used for the navigation—for example, in the event of a failure or behavior outside the specification or prediction of system components—and that the user can trust the navigation data, which is received from the satellites of the system by way of the satellite navigation signals. In particular, the user can rely on the accuracy of the received navigation data.
Prior art integrity concepts include the integrity concept of Galileo, the Wide Area Augmentation System (WAAS) and the European Geostationary Navigation Overlay Service (EGNOS). These integrity concepts demand a very comprehensive ground-based infrastructure in order to find an error in the navigation signals and then to warn the user in time. The ground-based infrastructure is very expensive for several reasons:                a) In order to be able to find errors in the navigation signals, the past concepts needed a close meshed network of observation stations.        b) In order to be able to evaluate the observations of the observation stations at a central center, a real time communication network is needed between the observation stations and the central processing center.        c) The information determined at the central processing center is disseminated globally over a communication network, in order to then disseminate from the ground to the end user over the selected satellites.        
Therefore, the present invention provides a method and a device for the efficient dissemination of information in a satellite navigation system.
This is achieved with a method for the efficient dissemination of information in a satellite navigation system as set forth in detail herein.
Exemplary embodiments of the present invention remove, from the system architecture, the demanding communication network for global dissemination of information determined by one or more central processing center(s) in order to simplify the ground infrastructure and, thus, make possible an efficient dissemination of information. At this point one approach for the dissemination of information to end users of the satellite navigation system includes, according to the invention, sending the information to be disseminated directly from a central processing center to selected satellites and passing the information from satellite to satellite until finally an adequate number of satellites can send the information to the utilization systems. This is performed to guarantee that the utilization systems are properly provided at a sufficiently high continuity with the information, especially for the integrity of the satellite navigation system. In addition to the considerably more efficient dissemination of information as compared to the prior art satellite navigation systems, the invention offers the advantage that ground-based communication networks, which are expensive to operate, can be simplified, in particular, decreased. In this context a ground-based communication network is also defined as a communication network that includes not only the cables and the radio relay links, but also communication over geostationary satellites.
One aspect of the invention involves a method for the efficient dissemination of information in a satellite navigation system, which includes a satellite system with a plurality of satellites, a network of observation stations for observing signals of the satellites, a central processing center for evaluating the observations of the observation stations and for generating information, based on the observations for dissemination to utilization systems, and a real time communication network for transmitting the observations from the observation stations to the central processing center.
The central processing center sends the information to selected satellites, and upon receiving the information, each of the selected satellites sends this information to the neighboring satellites.
In this way the information can be efficiently distributed in the satellite navigation system. Above all, the required ground-based infrastructure can be reduced and, thus, simplified.
According to another aspect of the invention, the selected satellites may be a subset of the satellites, which are directly visible from the central processing center, from the plurality of satellites.
Furthermore, one aspect of the invention provides that upon receiving the information, a selected satellite sends this information simultaneously to all of the satellites that are directly visible from the selected satellite. Accordingly, the time required for the dissemination of information is held to a minimum.
According to an additional aspect of the invention, a selected satellite can transmit the received information over an antenna, which has an antenna characteristic with a maximum in exactly or approximately the directions in which the neighboring satellites are the farthest away. Therefore, in contrast to a highly directive antenna, it is possible to disseminate the information in an efficient way to the neighboring satellites with as little technical complexity as possible.
According to one aspect of the invention, a selected satellite can transmit the received information over an antenna that is mounted on the earth side of the satellite. In this way it is possible to disseminate information to neighboring satellites that are at about the same orbital altitude as the satellite that is transmitting the information.
An additional increase in efficiency can be achieved by allowing a selected satellite to transmit, according to one aspect of the invention, the received information over several antennas. In this way the information can also be disseminated to the neighboring satellites that exhibit different orbital altitudes, in particular exhibit orbital altitudes that are different from the orbit of the satellites transmitting the information.
According to one aspect of the invention, each observation station can also evaluate a received satellite signal or several satellite signals or all of the receivable satellite signals of the satellite system and can send the information about the evaluation to all of the directly visible satellites, and each satellite can calculate its own integrity information using the received information.
Owing to the calculation of the integrity information in each receiving satellite, there is no need for a central determination of the integrity information and a corresponding dissemination to the satellites. In this way it is possible to further simplify the communication network for the dissemination of information to the satellites, since the only requirement is to configure the communication network in such a manner that the orbits and the clock parameters of the satellites can be determined, thus reducing even more the real time demands on the network.
Furthermore, the invention relates, according to an additional aspect, to a device for the efficient dissemination of information in a satellite navigation system, which includes a satellite system with a plurality of satellites, a network of observation stations for observing signals of the satellites, a central processing center for evaluating the observations of the observation stations and for generating information, based on the observations, for the dissemination to utilization systems, and a real time communication network for transmitting the observations from the observation stations to the central processing center.
Furthermore, the central processing center sends the information to the selected satellites, and upon receiving the information, each of the selected satellites sends this information to the neighboring satellites.
According to one aspect of the invention, the selected satellites may be a subset of the satellites, which are directly visible from the central processing center, from the plurality of satellites.
Furthermore, according to one aspect of the invention, a selected satellite can, upon receiving the information, send this information simultaneously to all of the satellites that are directly visible from the selected satellite.
According to an additional aspect of the invention, a selected satellite can also transmit the received information over an antenna, which has an antenna characteristic with a maximum in exactly or approximately the directions, in which the neighboring satellites are the farthest away. It may also be that the maximum of the antenna characteristic is adjusted only with respect to the elevation as a function of the distance from the other satellites.
Finally, according to one aspect of the invention, a selected satellite may also transmit the received information over an antenna that is mounted on the earth side of the satellite.
According to an additional aspect of the invention, a selected satellite may also transmit the received information over several antennas.
In a device, according to one aspect of the invention, each observation station may evaluate a received satellite signal or several satellite signals or all of the receivable satellite signals of the satellite system and send the information about the evaluation to all directly visible satellites, and each satellite may calculate, using the received information, its own integrity information and/or the integrity information for other satellites.
In an additional aspect, the invention relates to a satellite, for use with a device, that upon receiving the information from a central processing center, said device can transmit this information to neighboring satellites over an antenna, which is provided for this purpose.
One aspect of the invention provides that when the satellite antenna, which is provided for this purpose, is a horn antenna, which in the event of a special excitation in its center exhibits a minimum in the antenna characteristic and a maximum in exactly or approximately the directions, in which the neighboring satellites are the furthest away from the satellite.
Furthermore, according to one aspect of the invention, the antenna, which is provided for transmitting the information received from the central processing center, can be mounted on the earth side of the satellite.
In one aspect of the invention, solar collectors of the satellite may be designed in such a manner that they do not prevent the sending and receiving of information by way of the antenna, which is provided for transmitting the information received from the central processing center.
Finally, the satellite may exhibit, according to another aspect of the invention, a plurality of antennas, which are provided for transmitting the information received from the central processing center and which make possible the communication with satellites at other orbital altitudes.
Other advantages and potential applications of the invention under discussion are disclosed in the following description in conjunction with the embodiment depicted in the single drawing.